1. Field of the Invention
The present invention relates in general to automotive seat slide devices which move an automotive seat in a fore-and-aft direction and lock the same at a desired position, and more particularly to seat slide devices of a type which can prevent a dangerous position skip phenomenon of the seat which would occur when the seat is at an over-travel position.
2. Description of the Prior Art
One of the conventional seat slide devices of the above-mentioned type is disclosed in Japanese Patent First Provisional Publication No. 61-169340.
In the device diclosed in the publication, a latch member pivotally connected to an upper rail (viz., a movable rail fixed to a seat) is formed with two or three latch pawls which are latchingly engageable with latch holes formed in a side wall of a lower rail (viz., a stationary rail fixed to a vehicle floor). One of the latch pawls is formed longer and thinner than the other or others, so that when the seat comes to an over-travel position (viz., an abnormal extreme position where normal latching between the latch member and the latch holes fails to be established), at least the longer and thinner latch pawl establishes a latching engagement with an outermost hole of the latch holes. Thus, even when the associated vehicle is subjected to a rapid start or rapid braking, the seat at the over travel position is prevented from skidding rearwardly or forward.
However, due to inevitable errors in assembling the device, it sometimes occurs that even when the seat assumes the over travel position, not only the shorter latch pawl or pawls but also the longer latch pawl fails to establish a latching engagement with the associated latch hole, as is seen from FIG. 10. That is, the longer latch pawl (A) rides on a land portion of the side wall (C) disengaging from the outermost latch hole (B). Thus, under this condition, latching engagement is not established between the upper and lower rails, so that a dangerous seat skidding or position skip phenomenon tends to occur upon a rapid start or rapid braking of the vehicle.
One of measures for solving this dangerous matter is to increase the size or the width (L) of the outermost latch hole (B). This measure increases the chance of establishing the engagement between the longer and thinner latch pawl (A) and the hole (B).
However, as is known, formation of an enlarged hole in the side wall of the lower rail lowers the mechanical strength of the same.